After more than ten years development, radio frequency identification (RFID) technology which includes Integrated Circuit Card (IC), is now widespread used in modern daily life, for example, public transport system, entrance guard system, small electronic payment, and so forth. Radio frequency identification technology is one kind of automatic identification technology, which at least includes a tag and a reader. The tag is for storing electronic data in a determined format. In practice, the tag is usually attached on the surface of an object to be identified. The reader is also known as a readout, and is adapted for reading and identifying the electronic data stored in the tag without contacting the tag, thereby accomplishing the aim of identifying objects automatically. Furthermore, computers and computer networks are used to collect, process and transfer the identification information. Most RFID systems work under a fixed frequency and a set of standard protocols.
Digital modulation techniques are widely used in RFID, such as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK) modulation. ASK means that carrier amplitudes are defined as different values according to the modulation of digital data, for example, the carrier amplitude is “0” if the digital data is “0” in binary, and the carrier amplitude is “1” if the digital data is “1” in binary. Amplitude shifting is easy to implement, but it is susceptible to gain change. FSK means modulating carrier frequencies according to the digital data (“0” or “1”). For example, the carrier frequency is F1 if the digital data is “0” in binary, and the carrier frequency is F2 if the digital data is “1” in binary. FSK is good at anti-jamming, but needs to occupy a large bandwidth. PSK means modulating carrier phases according to the digital data. For example, the 180 phase shift represents “1”, while 0 phase shift represents “0”. PSK is best at anti-jamming, and the phase shift can be used as timing information to synchronize the clock of the sender and the receiver, and to speed up the data transferring. ASK, FSK and PSK are existing mature technologies and widely used in various communication systems.
Recently, with the development of rail transport, logistics management, goods security and individual identification, RFID technology has made great progress, and all kinds of RFID tags and identifying devices are needed. Usually, there is an electronic wallet in a tag and a cardholder needs to deposit some money in the tag. When a transaction occurs, the required money is deducted from the tag. But there are some drawbacks of a single function tag. For example, the cardholder has to go to a required place to deposit money, large transactions could not be protected by setting password, the RFID payment could not be combined with the mobile payment, and so on.
Meanwhile, after twenty years development, mobile communication terminal has become a necessary portable device almost by every consumer. Moreover, there is a trend that more functions would be integrated in a mobile communication terminal. It is common to utilize mobile phone networks to pay, such as GSM, CDMA. But how to combine mobile phones with tags and enable mobile phones to be used conveniently just like a bus card is a trend nowadays, and many equipment suppliers and mobile operators are trying to develop market in this field.
Being affected by the mobile phone payment in Japan and Korea, many operators have been expected to enter the field of small electronic payment. Non-contact proximity Radio Frequency Identification can provide effective solutions for real-time payment and on-site payment, and is considered to bring great opportunities to the mobile payment industry which is developing slowly at present. While a multi-purpose machine or a multi-purpose card which can combine mobile terminal and RFID technology is new trend in the next decade. Especially in the 3G era, RFID readers which can provide wireless-connectivity function and non-contact RFID are given priority. At present, there are two kinds of solutions for non-contact technology: Combi SIM card and Near Field Communication (NFC).
Combi SIM card is also known as dual interface SIM card, which means substituting a mobile phone inside SIM card with a Combi SIM card, and adding a non-contact IC card interface to the original contact SIM card. There are two typical solutions. One is printing the non-contact antenna of the non-contact IC card on a plastic film, and then pasting the plastic film onto the SIM card. The other one is the non-contact antenna of the non-contact IC card working as an independent component attached to front or rear of the mobile phone, and connected to the C4 and C8 interfaces which is not used yet. But there are some drawbacks for these two solutions. The antenna is easy to break when it is pasted to the SIM card or connected to the C4 or C8 interface. Furthermore, signals received by the dual interface SIM card or signals returned to the reader are extremely weak because of the shielding effect caused by the battery and the circuit board. Therefore, the communication quality between the dual interface SIM card and the reader is poor, and the reader almost can not receive the acknowledge signals from the dual interface SIM card.
NFC is a new solution about RFID technology provided by Nokia, Philips, and so on. The basic principle is to add a new RFID module adapted for payment to a redesigned mobile phone. The new RFID module communicates with the redesigned mobile phone according to a predetermined protocol. The drawback is that the consumers have to reform the mobile phones or buy a new mobile phone. This is not accepted by all consumers at the present and it is a great waste of resources.
FIG. 1 shows a schematic diagram of the structure of a typical dual interface IC card in prior art, and FIG. 2 shows a schematic diagram of the RF interface circuit of a typical dual interface IC card in prior art. Referring to FIG. 1, it is provided by Gemplus. The contact part works according to the ISO/IEEC 7861 standard protocol, while the non-contact part works according to the ISO/IEEC 14443 TYPEA/TYPEB standard protocol. The dual interface IC card comprises: a Radio Frequency (RF) interface, a Central Processing Unit (CPU), an interrupt processing module, a random number generator, a read-only memory (ROM), an EEPROM, an external RAM, a Cyclic Redundancy Check (CRC) module, a timing module and a ISO/IEEC 7816 module. The RF interface is the communication interface between the dual interface IC card and a reader whose frequency is 13.56 MHz. CPU works as the central processing unit, and finishes the communication and transaction with the reader, together with the internal software. The interrupt processing module handles various interrupts generated by peripherals. The ROM stores the internal firmware program. The EEPROM and external RAM store data of the dual interface IC card and intermediate variables. The CRC module generates cyclic redundancy check code and ensures the data integrity in communication. The timing module provides an internal clock for the inside modules. The ISO/IEEC 7816 module is the communication interface between the mobile phone and the dual interface IC card, and is the channel through which the mobile phone supplies power for the dual interface IC card.
Referring to FIG. 2, the RF interface comprises: a non-contact antenna whose frequency is 13.56 MHz, a demodulation circuit, a digital quantizing circuit and a modulation circuit.
The signals sending from the reader to the dual interface IC card, which are 100% ASK modulation signals, are received by the non-contact antenna. The demodulation circuit in the dual interface IC card demodulates the signals by the way of diode peak envelope demodulation. The demodulated signals are transferred to the digital quantizing circuit for quantification process, and then generating baseband signals. The baseband signals are transferred to the CPU for processing.
Before the CPU sends acknowledge signals to the reader, the CPU completes coding first, and then sends them to the modulating circuit for modulating. After that, the acknowledge signals are transmitted by adjusting the resistors in the modulation circuit of the RF interface.
Because of the shielding effect of the battery and the circuit board in the mobile phone, if the dual interface IC card is applied in the mobile phone instead of the internal SIM card, the dual interface IC card can not reliably receive the command sent form the reader. Meanwhile, because the acknowledge signals are attenuated significantly, the reader can not receive and distinguish the acknowledge signals sent from the dual interface IC card.